Foamable composition comprising a thermoplastic polymer and barium azocarbonate and method of foaming



United States Patent FOAMABLE COMPOSITION COMPRISING A THER- MOPLASTIC POLYMER AND BARIUM AZOCAR- BONATE AND METHOD OF FOAMING Henry A. Hill, Watertown, Mass., assignor, by mesne assignments, to National Polychemicals, Inc. No Drawing. Filed July 7, 1959, Ser. No. 825,413 4 Claims. (Cl. 260-25) This invention relates to the production of cellular plastomeric products, including sponge rubber or cellular rubber made from natural or synthetic rubber, as well as foam masses of other plastics, resins, and the like.

A major scientific achievement in the plastics field has been the development of the hydrocarbon polymers, such as polyethylene and polypropylene. These developments have included the Ziegler, Natta, and Phillips Processes, and as applied to polyethylene have resulted in a highmelting, higher-density product. Owing to the higher melting points of materials, such as the high-density polyethylenes and the polypropylenes, efforts to produce blown foams and sponges from these materials have not been successful. In certain applications, processing temperatures in the range of ISO-500 F. are required, and hitherto no blowing agent has been available which is operable in this processing range.

The present invention provides a blowing agent suitable for use with high melting polymers such as polyethylene (melting point 255265 F.), polypropylene (melting point 325-340 F.) and Type 6 nylon, which is derived from caprolactam (melting point 390-425 F.). The blowing agent of this invention is also suitable for use in blowing other plastomers such as rubber, vinyl resins, and other thermoplasticssuitable for the production of blown products. The blowing agent utilized in this invention is barium azocarbonate, which it has been found will readily disperse inthe stock by conventional means and is moreover economical, and-of good stability. The decomposition ofbarium azocarbonate will occur at temperatures as high as 4-75525 F., but lower blowing temperatures will also be. provided for by incorporating other compounds containing acidic or active hydrogens, such as stearic acid or ethylene glycol.

In practice the barium azocarbonate, in an amount to produce the desired degree of blowing, typically between 1 and parts per 100 parts of plas'tomer, is mixed uniformly into the plastomer which is then sheeted or otherwise formed to the desired shape and then heated to activate the blowing agent. The blown product is odorless and of uniform closed cell structure and is not at all discolored by the blowing agent.

A particularly advantageous property of-hydrocarbon polymers, such as polyethylene and polypropylene blown with barium azocarbonate, is a markedly improved stability against degradation that normally occurs in the presence of heat and light. An important field of application for these blown high melting hydrocarbon polymers is in wire coating where advantage may be taken of the good electrical properties, such as low dielectric constant, and low power factor loss, possessed by mater. CC

rials of this type. Blown hydrocarbon polymers have not only the desirable electrical properties but their use also means that less material is required and improved flexibility of the coated wire is obtained.

Although barium azocarbonate is known in the art, a product suitable for the present invention is preferably produced directly by the reaction between barium oxide and azodicarbonamide according to the reaction The production of barium azocarbonate and its use in numerous types of plastomer compositions are described in detail below. The examples herein are presented as exemplary of this invention, and it is contemplated that the formulations given may be modified in accordance with the understanding of those skilled in the art and familiar with this disclosure.

PREPARATION OF BARIUM AZOCARBONATE Example I To 4500 parts of water are added 361 parts of commercial barium oxide. The rnixture is heated to C. and filtered, giving a solution containing 344 parts of barium oxide, havinga pH of 12.8. The water insoluble filter residue is discarded. After the filtered solution has been cooled to 25 C;, 247.8 parts of the azodicarbom the filter to retain about 1 part of the mother liquor for 1%. of the product, asopposed to a pl-I of, 12.8 of the starting solution.

The mother liquor has a pH of 11.4 The wet filter cake is either washed with acetone, or alterna-.

tively-reslurried in acetone and re-filtered, and then subsequently dried. Two parts of' the dried product resl urried in parts of water gives a pH of 9.5.

Exam ple II The procedure given above is followedwith the exception that the filtered. solution of. barium. hydroxide is cooled to the temperature range of 3 C. to 10 C. before the addition of the a zodicarbonamide. The progress of the reaction followed as before by the differential solubility of azodicarbonamide aadbarium azocarbonate indimethyl sulfoxide, gives the following results: Atthe end of 2 hours, 25% unreacted; at the endof 4 hours, 20% unreacted; at the end of 6 hours, 15.2% unreacted;

at the end of 8 hours, 9.3% unreacted; at the end of 10 hours, 0.7% unreacted; at the end of 12 hours, 0.7% unreacted. The bath is held at temperatures of between 3 C. to 10 C. for 12 hours, filtered, sucked dry, either washed with or re-slurried in acetone and filtered and then dried. The product of previous run has a deep yellow color; the product of present yellow color, indicating that the run has a very light product made at the lower temperature has a much finer particle size.

PRODUCTION OF BLOWN PLASTOMERS Example I The effectiveness of barium azocarbonate as a blowing agent for polyolefin resins is shown in the following 15 formulations:

Parts by Weight Test 0 Test D Test E Ingredient:

DYNH-l Marlex 50 Pro-Fax Barium azocarbon Specific gravity, 70 F./70 F. (calculated) Temperature, F. Time minutes Specific gravity, 70 F./70 Color 0. 94 0. 9s 0. 93 475 525 525 10 10 10 0.58 0. 60 0. 44 White White White e Low density polyethylene. b High density polyethylene. e Polypropylene.

The resin was heated to its melting point on the rolls of steam-heated rubber mill. When molten, the blowing agent was incorporated and mixing continued until good dispersion was obtained. The mixture of resin and blowing agent was sheeted from the mill, cooled, and cut into sections. To expand the plastic,

the mixture of plastic and blowing agent was heated in a 3 x 3 x 0.075 mold to the desired temperature under a pressure of 940 p.s.i. and held for the indicated time. The pressure was then reduced to atmospheric and the plastic was permitted to expand. The mold was cooled and the blown sample withdrawn.

When the mold cavity was filled to only of its volume, the pressure was not released to permit expansion but the full pressure of 940 p.s.i. was maintained throughout the cycle, the pressure being dropped 50 only after cooling.

Example II Polypropylene was tumbled with 2% of its weight of barium azocarbonate. The mixture of plastic and blowing agent was fed to a cross-head extruder for coating on wire. It was found under the that barium azocarbonate starts to conditions of the test decompose at 492 F.

The best results were obtained in the following operating conditionsforward pressure 2000# p.s.i., medium pressure 1600# p.s.i., stock temperature 538 F., the head temperature of 520 F. Temperature in Zone 1, 500

F.; temperature in Zone 2, 430 F.;

screw speed, 43 r.p.m.

It is to be noted that while polypropylene was being expanded with barium azocarbonate, dicated that no more than 0.5 to a tests were run that inmaximum of one part of carbon monoxide per ten thousand parts of air were detected in the vicinity of the extruder head. This is well within the allowable maximum of million.

Example III one hundred parts per The elfectiveness of barium azocarbonate as a blowing agent for a styrene-butadiene rubber is shown by the following formulations:

Zinc oxide Processing oil, light. Petrolatum Processing oil, mediurrn. Antioxidant, non-staining" Phthalic anhydride. Stearic acid Diethylene glycol The bath temperature was then maintained at 150 F. and then were added:

Dibcnzothiazyldisulfide Diorthotolylguanidine... Zinc salt mereaptobenzotluazole Barium Azocarbonate Specific gravity, 70 F./70 F. Calculated Cure: Cold-pressed in 3 x 3 x 0.250 cavity at 2600 p.s.i. on the area of the cavity, then 355 F heated (confined). Specific gravity 70 F./70 F. after cure and 0.49

expansion. Cell structure Very line Very fine.

Styrene, 23.5, butadiene 76.5 polymerized at 43 F. to a Mooney viseosity (ML4 at 212 F.) of 50.

b Styrene 23.5, butadiene 76.5 polymerized at 122 F. to a Mooney viscosity (ML4 at 212 F.) of 30.

c Styrene 23.8, butadiene 76.2, non-staining antioxidant, to a Mooney viscosity (MM at 212 F.) of 35.

d Styrene 85, butadiene 15 copolymer.

8 Plus 2.5 hours 250 F. (unconfined in oven).

Example IV The efiectiveness of barium azocarbonate as a blowing agent for Neoprene W is shown in the following formulations Parts by Weight Test H Test I Ingredient:

Neoprene W B Stearic acid. Parafiin wax Anti nrirl ant Magnesium oxide, extra light Medium thermal carbon black.

H O s pes s rp 00000000 Was blended on a r a temperature of approximately F. for 2 minutes. Carbon blacks, processing oils miscellaneous fillers and pigments added and mixed and blended and stock temperature maintained at 200 F. Mill was then cooled and batch temperature maintained at a maximum of F. and then were added:

Barium Azocarbonate 2-Mereaptoimidazo S eciflc gravity, 70 F./70 F urlng conditions: Cold pressed in a 3 x 3 x 0.250 mold at 2800 p.s.i. on the area of the mold, then heated.

Sjpccific gravity, 70 F./70 F ure Specific gravity, 70 F./70 F B A polychloroprene. b Unconfined.

Example V The efiectiveness of barium azocarbonate as a blowing agent for butyl rubber is shown in the following formulations:

Parts by Weight Test .1 Test K Ingredient:

Butyl 365 Fine extrusion furnace carbon black Medium thermal carbon black Paraifinic oil Paraffinie wax Diethyleneglycol Butyl was blended on a 2-roll mill at a temperature of 100 F. for 2 minutes. Carbon blacks, processing oils, miscellaneous fillers and pigments added and mixed and blended. Stock temperature reached 200 F. and was held there 3 minutes to insure good dispersion. Mill was then cooled and batch temperature maintained at 150 F. maximum and then were added:

Tetra methyl thiuram dlsulfi'de Zino salt, mercaptobenthiazole Barium Azocarbonate 1. Sulfur A copolymer of isobutylene (97%) and isoprene (3%).

Unconfirmed.

Examples III through V illustrate the use of barium azocarbonate in polymers other than the high melting hydrocarbon polymers. These examples show that these polymers, conventional butadienestyrene synthetic rubber, butyl rubber, neoprene, a poly (vinyl chloride) plastisol and a poly (vinyl chloride) sheet may be blown to desirable reduced densities by the means of barium azocarbonate.

It is noted that the temperature ranges in which these five materials have been blown are Well below the range desired for the high melting hydrocarbon polymers, due to the presence of activators such as stearic acid, ethylene glycol, and the like.

20.0 Med. fine. Med. fine.

Although this invention is described with specific reference to preferred embodiments, it is contemplated that modifications will readily occur to those skilled in the art and familiar with this disclosure. It may be found, for instance, desirable to use smaller amounts of blowing agent, perhaps as little as 0.1 part per parts of plastomer, or higher amount such as 25 parts per 100 parts of plastomer in certain specific formulations. Other plastomers, other than those specifically enumerated, and mixtures of plastomers may also be found suitable for particular uses of this invention. It is contemplated that such a modification may be made without departing from the scope of the invention.

Having thus disclosed my invention and described in detail preferred embodiments thereof, I claim and desire to secure by Letters Patent:

1. A composition suitable for blowing comprising a thermoplastic polymer derived from an ethylenically unsaturated monomer and barium azocarbonate dispersed therein in an amount efiective to produce cells in said thermoplastic polymer.

2. The composition defined by claim 1 wherein the thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene, copolymers of styrene and butadiene, polychloroprene, poly (vinyl chloride), natural rubber, and isobutylene-isoprene butyl rubber copolymers.

3. The method of forming blown thermoplastic polymer derived from ethylenically unsaturated monomers comprising mixing the thermoplastic with barium azocarbonate and heating the mixture to a temperature sufficient to decompose the barium "azocarbonate.

4. The method defined by claim 3 wherein the thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene, copolymers of styrene and butadiene, polychloroprene, poly (vinyl chloride), natural rubber, and isobutylene-isoprene butyl rubber copolymers.

References Cited in the file of this patent UNITED STATES PATENTS 2,256,483 Johnston Sept. 23, 1941 2,496,255 Von Glahn Jan. 31, 1950 2,599,299 Upson June 3, 1952 2,739,134 Parry et al Mar. 20, 1956 2,901,446 Hawkins Aug. 25, 1959 OTHER REFERENCES Thiele: Justus Liebigs Annalen der Chemie, volume 271, page 133 (1892).

Lally et 211.: Modern Plastics, volume 27, pages 111- 112 (1949).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 141,002 July l4 1964 Henry A, Hill It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, footnote "b" of the table in Example V, for "Unconfirmed" read v Unconfined -u Signed and sealed this 29th day of December 1964,

(SEAL) Attest- ERNE ST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A COMPOSITION SUITABLE FOR BLOWING COMRISING A THERMOPLASTIC POLYMER DERIVED FROM AN ETHYLENCIALLY UNSATURATED MONOMER AND BARIUM AZOCARBONATE, DISPERSED THEREIN IN AN AMOUNT EFFECTIVE TO PRODUCE CELLS IN SAID TERMOPLASTIC POLYMER. 